Depth of Field vs. Shutter Speed
/Jul/07 Filed in: Tips and
tricks
In the first installment of Merrifield Photography
Tips, we talked about basic composition and the rule
of thirds. No doubt this improved your picture taking
a great deal, but hopefully it has left you hungry
for more. Well I just happen to have a few more
tricks up my sleeve that I am confident you will pick
up with no difficulty. Now understand that this next
technique is a little more advanced, and will require
that your camera be equipped with a few more advanced
features, but we will get to that later.
As you have figured out by the title, we are going to discuss depth of field, shutter speed, and the intertwined relationship they share with light. A comment I often hear is, “My picture didn't turn out the way I thought it would when I shot it.” This is a common complaint by many photographers, amateur and pro alike, and there are many factors that contribute to this phenomenon, but I feel the strongest cause for this is depth of field. For those of you that are unfamiliar with this term, depth of field or DOF as I will refer to it from here on out, is the range or distance in front of, and behind your point of focus that still maintains relative sharpness. For example, if I take a picture of your face, I will focus on your eyes (which will always be the point of focus in a good portrait). If the end result shows that the tip of your to nose to the back of your ear is in focus than I am shooting with a greater DOF than if only your eyes were in sharp focus.
Still confused? Try this: stand at one of a room, pick an object somewhere in the middle of the room, and with your naked eye, focus on that object. Without taking your eye off the object, try and notice your surroundings. How much is in focus? Very little, right? Your eyes are demonstrating a shallow depth of field. Now, take a look at a painting. A nice landscape painting, like the kind you find being sold out of the back of a van at the corner gas station, by a “starving artist” (come on, we all have one of those kicking around in the closet somewhere). As you let your eyes wonder across the painting, you'll notice that every object in the painting is in focus; from the little flower beside the cottage in the foreground, to the snowcapped mountains in the background. This is an example of maximum DOF. Shallow DOF = very little in focus. Greater DOF = lots in focus. Got it?
Now with that being said, you ask, “How do I control the DOF?” Well if you look into your cameras operating manual you will hopefully find a section about aperture settings. Now don't worry about what an aperture is at this point, just try to remember that your aperture is represented by an f-stop. If your camera is equipped to adjust this aperture (or f-stop) then it is by this adjustment that you can control the DOF. Now, a more complicated text would go on to explain that an f-stop is a ratio of focal length to aperture diameter, where f2 = 1/2, and if applied to a lens with a 100mm focal length would be the equivalent to an aperture diameter of 50mm, and f4 would be 25mm and so on... but what does this really mean to you? Instead, I would like to spell it out in a way that make total sense and is very easy to learn. All you need to remember is that like quantitative terms belong together. So far, I have taught you that:
A shallow (or small) DOF = very little in focus
A greater (or big) DOF = a lot in focus
Now let's add the next part of the equation:
A small f-stop (i.e. f2) = a shallow (or small) DOF = very little in focus
A large f-stop (i.e. f32) = a greater (or big) DOF = a lot in focus
Seems easy enough right? So what's the catch? The catch is that the DOF you desire must be attainable within the light you have available to you. If you are working with a flash, then you have more flexibility. If, however, you are working with the natural or available light around you then your choices become fewer. This is due to a nasty thing called exposure. A proper exposure is made up of three components; your f-stop, your shutter speed, and the amount of light you have at your disposal. Add all of these up and factor in a few light sensitivity ratings expressed in iso values (i.e. iso 100, iso 400 and so on... I'm sure you have seen this before), and you have the makings of a University masters degree in obscurity and confusion.
Lets simplify, shall we? Lets say you want to take a picture of grandma, but grandma is standing 8 feet in front of a graffiti covered brick wall (yeah, grandma's 'hood has taken a turn for the worse). Obviously (for me anyway) you don't want the graffiti in focus, so you decide to shoot the picture with a small f-stop to minimize the DOF so that grandma's face is in focus and not the graffiti. So now that you have changed the f-stop you have to account for the other two components in a proper exposure; shutter speed, and light. Lets assume that the light hasn't changed, so all we need be concerned with is the shutter speed. At this point I could break into the theories of exposure and the reciprocal relationship between aperture and shutter speed, but instead I am going to return to the formulas we have been building, but this time we will add the shutter speed:
A short shutter duration = a small f-stop = a shallow DOF = very little in focus (a working exposure example: 1/8000 of a second at f2)
A long shutter duration = a large f-stop = a greater DOF = a lot in focus (a working exposure example: 1/30 of a second at f32)
(Incidentally, on a sunny day, with iso 100 film, both of the above examples amount to an EV (or "Exposure Value") of zero as per the “Sunny 16” rule...but we will leave that for another lesson)
So with all else equal, what ever you do to adjust the aperture, you must also make an equal adjustment to your shutter speed. Fortunately many cameras are built with automatic options that compensate one parameter for any adjustments that you have made to the other, so you really won't have to worry yourself with too many technical details.
In closing, let's recap what we have learned here.
If you want your main subject to be in focus but the background to be blurry, you must:
use a small f-stop number, and a short shutter duration to get a shallow depth of field so that very little is in focus.
If you want everything in the shot to be crystal clear, you must:
-use a large f-stop number, and a long shutter duration, to get a large depth of field so that lots is in focus.
I hope you enjoy learning to use this technique, and I hope you become a better photographer for it. Happy shooting to you, and be sure to stay tuned for more helpful hints from Merrifield Photography.
As you have figured out by the title, we are going to discuss depth of field, shutter speed, and the intertwined relationship they share with light. A comment I often hear is, “My picture didn't turn out the way I thought it would when I shot it.” This is a common complaint by many photographers, amateur and pro alike, and there are many factors that contribute to this phenomenon, but I feel the strongest cause for this is depth of field. For those of you that are unfamiliar with this term, depth of field or DOF as I will refer to it from here on out, is the range or distance in front of, and behind your point of focus that still maintains relative sharpness. For example, if I take a picture of your face, I will focus on your eyes (which will always be the point of focus in a good portrait). If the end result shows that the tip of your to nose to the back of your ear is in focus than I am shooting with a greater DOF than if only your eyes were in sharp focus.
Still confused? Try this: stand at one of a room, pick an object somewhere in the middle of the room, and with your naked eye, focus on that object. Without taking your eye off the object, try and notice your surroundings. How much is in focus? Very little, right? Your eyes are demonstrating a shallow depth of field. Now, take a look at a painting. A nice landscape painting, like the kind you find being sold out of the back of a van at the corner gas station, by a “starving artist” (come on, we all have one of those kicking around in the closet somewhere). As you let your eyes wonder across the painting, you'll notice that every object in the painting is in focus; from the little flower beside the cottage in the foreground, to the snowcapped mountains in the background. This is an example of maximum DOF. Shallow DOF = very little in focus. Greater DOF = lots in focus. Got it?
Now with that being said, you ask, “How do I control the DOF?” Well if you look into your cameras operating manual you will hopefully find a section about aperture settings. Now don't worry about what an aperture is at this point, just try to remember that your aperture is represented by an f-stop. If your camera is equipped to adjust this aperture (or f-stop) then it is by this adjustment that you can control the DOF. Now, a more complicated text would go on to explain that an f-stop is a ratio of focal length to aperture diameter, where f2 = 1/2, and if applied to a lens with a 100mm focal length would be the equivalent to an aperture diameter of 50mm, and f4 would be 25mm and so on... but what does this really mean to you? Instead, I would like to spell it out in a way that make total sense and is very easy to learn. All you need to remember is that like quantitative terms belong together. So far, I have taught you that:
A shallow (or small) DOF = very little in focus
A greater (or big) DOF = a lot in focus
Now let's add the next part of the equation:
A small f-stop (i.e. f2) = a shallow (or small) DOF = very little in focus
A large f-stop (i.e. f32) = a greater (or big) DOF = a lot in focus
Seems easy enough right? So what's the catch? The catch is that the DOF you desire must be attainable within the light you have available to you. If you are working with a flash, then you have more flexibility. If, however, you are working with the natural or available light around you then your choices become fewer. This is due to a nasty thing called exposure. A proper exposure is made up of three components; your f-stop, your shutter speed, and the amount of light you have at your disposal. Add all of these up and factor in a few light sensitivity ratings expressed in iso values (i.e. iso 100, iso 400 and so on... I'm sure you have seen this before), and you have the makings of a University masters degree in obscurity and confusion.
Lets simplify, shall we? Lets say you want to take a picture of grandma, but grandma is standing 8 feet in front of a graffiti covered brick wall (yeah, grandma's 'hood has taken a turn for the worse). Obviously (for me anyway) you don't want the graffiti in focus, so you decide to shoot the picture with a small f-stop to minimize the DOF so that grandma's face is in focus and not the graffiti. So now that you have changed the f-stop you have to account for the other two components in a proper exposure; shutter speed, and light. Lets assume that the light hasn't changed, so all we need be concerned with is the shutter speed. At this point I could break into the theories of exposure and the reciprocal relationship between aperture and shutter speed, but instead I am going to return to the formulas we have been building, but this time we will add the shutter speed:
A short shutter duration = a small f-stop = a shallow DOF = very little in focus (a working exposure example: 1/8000 of a second at f2)
A long shutter duration = a large f-stop = a greater DOF = a lot in focus (a working exposure example: 1/30 of a second at f32)
(Incidentally, on a sunny day, with iso 100 film, both of the above examples amount to an EV (or "Exposure Value") of zero as per the “Sunny 16” rule...but we will leave that for another lesson)
So with all else equal, what ever you do to adjust the aperture, you must also make an equal adjustment to your shutter speed. Fortunately many cameras are built with automatic options that compensate one parameter for any adjustments that you have made to the other, so you really won't have to worry yourself with too many technical details.
In closing, let's recap what we have learned here.
If you want your main subject to be in focus but the background to be blurry, you must:
use a small f-stop number, and a short shutter duration to get a shallow depth of field so that very little is in focus.
If you want everything in the shot to be crystal clear, you must:
-use a large f-stop number, and a long shutter duration, to get a large depth of field so that lots is in focus.
I hope you enjoy learning to use this technique, and I hope you become a better photographer for it. Happy shooting to you, and be sure to stay tuned for more helpful hints from Merrifield Photography.